1. Field of the Invention
The present invention relates to a reverse conducting semiconductor device for use in home electric appliances, electric motor vehicles, railroad systems, solar or wind power systems, etc.
2. Background Art
Japanese Patent Laid-Open No. 2013-197122 discloses a reverse conducting semiconductor device (a reverse conducting insulated gate bipolar transistor (RC-IGBT)). The reverse conducting semiconductor device has an IGBT and a diode (free wheeling diode (FWD)) formed on one semiconductor substrate. In the reverse conducting semiconductor device disclosed in Japanese Patent Laid-Open No. 2013-197122, a p-anode layer and a p+-anode layer are provided as an anode layer for the diode and an ohmic contact is established between the p+-anode layer and an emitter electrode.
In a case where trench gates are formed in the entire surface of the semiconductor substrate, the trench gate interval may be reduced in order to reduce the area of the anode layer so that the performance of the diode is improved. If the trench gate interval is reduced, it is difficult to connect the anode layer and the emitter electrode by a contact electrode formed of aluminum for example. It is, therefore, preferable to connect the anode layer formed between the trench gates and the emitter electrode by tungsten plugs. If tungsten plugs are used, a barrier metal is provided between the tungsten plugs and the anode layer to prevent a material in the tungsten plug from diffusing into the semiconductor substrate (anode layer).
The width of contacts between the barrier metal and the anode layer is smaller than the trench gate interval. Therefore, if the p+-anode layer (a high-concentration anode layer) is formed in island form as viewed in plan as disclosed in Japanese Patent Laid-Open No. 2013-197122, there is a problem that the area of contact between the barrier metal and the high-concentration anode layer is changed when the tungsten plug forming position is shifted. This change in contact area can be a cause of a variation in characteristic of the diode.